Objectives - This research will assess the effectiveness of psychiatric consultation-liaison (CL) in a primary care setting through a randomized trial. The trial will measure the effectiveness of CL in reducing psychiatric symptoms, use of services, other illness behaviors, and health care costs among frequent users of heath care. Secondary objectives will be to describe the DSM-III diagnositic status of screened high utilizers of health care and to compare the Hopkins Symptom Checklist and patients' primary care physician in selection of patients appropriate for psychiatric intervention. Subjects - This study will be carried out in two primary care clinics of Group Health Cooperative of Puget Sound. Subjects will be patients with 10+ visits in the prior year regarded as likely to benefit from CL services. Design - about 1000 high utilizers will be screened for referral for CL evaluation by the SCL and by primary care phyician assessment. From among these screened patients 120 eligible and consenting patients will be assigned at random to receive a conjoint CL evaluation and 120 to usual care. The CL evaluation will employ the DIS to structure the examination and diagnoses will be made using DSM-III checklists. Management strategies will be identified based on the results of the evaluation and will include treatment of mental disorders, management of somatization, modification of illness behavior. Patient managment will be carried out according to guidelines designed for implementation by primary care physicians. Measures - Outcomes will be assessed 3, 6 and 12 months after randomization and will be measured by patient questionnaire, utilization data, physician assessment and abstraction of medical records. The major outcome variables will be psychiatric symptom levels as measure by the SCL, use of services, associated illness behaviors, health care costs and satisfaction with health care services. Effects of CL on providers will be assessed by pre and post-study questionnaire in comparison to a matched sample of non-participating physicians.